Cool now, 50s by Sunday. 70 returns next Friday?

Ah, springtime in Minnesota. Two steps forward. One step back.

That's the usual state of affairs as we stumble forward into spring and eventually summer. Warm front. April showers. Blustery cold front. Steel gray sky. Lather, rinse, repeat.

We ride Minnesota temperature roller coaster in the next week. We're on the downslope into Saturday. Temps spike back into the 50s briefly Sunday in southern Minnesota, as a Clipper brings a quick shot of snow to the north. Signs of a more significant warm-up, and another shot at 70 degrees are on the horizon a week from Friday.

Soaking rains

This was a good soaking rain for Minnesota. It's interesting that systems like this usually come in multiple waves. Fronts and upper air waves often drive multiple precip bands as low pressure system roll through. The 24-hour radar history confirms two primary rain waves.

As advertised, many locations picked up over .50" with some higher totals around southern Minnesota. Here are some selected preliminary totals. We'll add to these slightly over the next 24 hours.

Fast track

Quick weather changes ahead in the next 3 days as a fast moving jet stream overhead drives minor weather features. One low brings spotty showers Thursday. Another brings light snow to northern Minnesota Friday.

Here's a more detailed breakdown of the forecast for the next week. Sunday's highs on this chart could be conservative. I won't be surprised to see bank thermometers flashing numbers in the 50s Sunday afternoon. The Euro suggests 60 but I'm not sold on that yet. Stay tuned.

Warmer next week?

Signs point to milder air again next week as upper winds blow form the Pacific once again.

NOAA's climate group agrees, another wave of milder than average air invading from the west.

NOAA's GFS model is cranking out temperature near 70 again by next Friday April 8th, followed by a potentially wet weekend.

Weather Wars: Why the European model still leads

Volvo. Guinness. Ikea?

There are some things Europe just seems to do well. Add numerical weather forecasting to the list. Here's a good update from Physics Today on why even though NOAA's weather forecast models are  making strong gains, the European Centre for Medium Range Weather Forecasting is still the best on the planet overall.

A critical part of the European center’s performance is its method for incorporating information from worldwide weather observations. “The ECMWF is recognized as being at the forefront of how to do that data assimilation to get the most from the observations,” Thorpe says. The center uses a mathematical method called four-dimensional variational data assimilation, or 4D-Var, in which the fourth dimension is time. “We take our observations not at just a single time but over a window of several hours,” Thorpe explains. “Information from prior short-range forecasts is merged with the observations.”

The Met Office also uses 4D-Var. But the GFS model, operated by the US National Weather Service’s (NWS) National Centers for Environmental Prediction (NCEP), uses a somewhat less advanced 3D assimilation system. “Implicitly, a 4D-Var is much more accurate than the 3D-Var method, but the problem is that it is 10 times more expensive to run,” says Hendrik Tolman, director of the NCEP’s Environmental Modeling Center. “You have to be able to run your model forward and backwards, and you need a separate version of the model to do that.”

The NCEP has been making what Tolman calls incremental improvements to the GFS, including a recent boost to its horizontal spatial resolution in forecasts out to 10 days ahead from its previous 27-km-scale global grid to a 13-km grid. That is slightly higher than the ECMWF’s 16 km. “We made [the GFS] better by going to the higher resolution, and we also spent quite a bit of effort to go to better ways of starting off the model with all of the observations we have,” he says.

The acquisition last year of two Cray supercomputers tripled the NCEP’s computing capacity and enabled the refined grid size. Congress provided funding for that upgrade in the wake of Sandy. A similar jump in computing performance expected next year will bring the NCEP’s computing assets into rough parity with those of the ECMWF. But both Tolman and Thorpe agree that an apples-to-apples comparison isn’t meaningful because the NCEP’s computers need to work on a lot more problems than just the medium-range global weather prediction that is the ECMWF’s mission.